Diagnostic Test

WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

1) A/C PRESSURE TRANSDUCER VOLTAGE BELOW 0.6 OF A VOLT
NOTE: Make sure the A/C refrigerant System is properly charged per Service Information.

Start the engine.

With a scan tool, read the A/C Pressure Sensor voltage.

Is the voltage below 0.6 of a volt?

Yes
1. Go To step 2).
No
1. Refer to INTERMITTENT CONDITION .
2. Perform POWERTRAIN VERIFICATION TEST .
2) (F891) 5-VOLT SUPPLY CIRCUIT

Fig 1: Checking 5-Volt Supply Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Turn the ignition off.

Disconnect the A/C Pressure Transducer harness connector.

Ignition on, engine not running.

Measure the voltage on the (F891) 5-volt Supply circuit in the A/C Pressure Transducer harness connector.

Is the voltage between 4.5 to 5.2 volts?

Yes
1. Go To step 3).
No
1. Go To step 6).
3) A/C PRESSURE TRANSDUCER
With the scan tool, monitor the A/C Pressure Transducer voltage.

Is the voltage above 0.6 of a volt?

Yes
1. Replace the A/C Pressure Transducer.
2. Perform POWERTRAIN VERIFICATION TEST .
No
1. Go To step 4).
4) (C18) A/C PRESSURE SIGNAL CIRCUIT SHORTED TO GROUND

Fig 2: Checking A/C Pressure Sensor Signal Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Turn the ignition off.

Disconnect the C1 FCM harness connector.

Measure the resistance between ground and the (C18) A/C Pressure Signal circuit in the A/C Pressure Transducer harness connector.

Is the resistance below 100 ohms?

Yes
1. Repair the short to ground in the (C18) A/C Pressure Signal circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
No
1. Go To step 5).
5) (C18) A/C PRESSURE SIGNAL CIRCUIT SHORTED TO THE (C918) SENSOR RETURN CIRCUIT

Fig 3: Checking A/C Pressure Sensor Signal Circuit & Sensor Ground Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Disconnect the IPM FCM harness connector.

Measure the resistance between the (C18) A/C Pressure Signal circuit and the (C918) Sensor Return circuit in the A/C Pressure Transducer harness connector.

Is the resistance below 100 ohms?

Yes
1. Repair the short between the (C918) Sensor Return circuit and the (C18) A/C Pressure Signal circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
No
1. Go To step 8).
6) (F891) 5-VOLT SUPPLY CIRCUIT OPEN

Fig 4: Checking A/C Pressure Sensor 5-Volt Supply Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Turn the ignition off.

Disconnect the C1 FCM harness connector.

Measure the resistance of the (F891) 5-volt Supply circuit from the A/C Pressure Transducer harness connector to the C1 FCM harness connector.

Is the resistance below 5.0 ohms?

Yes
1. Go To step 7).
No
1. Repair the open in the (F891) 5-volt Supply circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
7) (F891) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND

Fig 5: Checking 5-Volt Supply Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Measure the resistance between ground and the (F891) 5-volt Supply circuit in the A/C Pressure Transducer harness connector.

Is the resistance below 100 ohms?

Yes
1. Repair the short to ground in the (F891) 5-volt Supply circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
No
1. Go To step 8).
8) FRONT CONTROL MODULE
NOTE: Before continuing, check the FCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.

Were there any problems found?

Yes
1. Repair as necessary.
2. Perform BODY VERIFICATION TEST - VER 1 .
No
1. Replace and program the Front Control Module per Service Information.
2. Perform BODY VERIFICATION TEST - VER 1 .